495 results about "Neutral point voltage" patented technology

The invention provides a low current grounding single phase earth fault diagnosis method, comprising: capturing A voltage to ground, B voltage to ground, C voltage to ground, neutral point current and entire waveform information of each zero sequence current from a steady state to a transient state then to steady state when neutral point voltage exceeds presupposed threshold; first diagnosing whether being single phase earth fault, PT fusing, ferro resonance, arc suppressing coil resonance overvoltage, or neutral point overvoltage disturbance caused by experiment; selecting lines for the earth fault. The inventive method makes full use of steady state information and transient information of electric network before and after fault, and judges the fault and selects lines according to the long term changing rule of the neutral point voltage, which is different from the traditional stable state line selecting method and the transient line selecting method, thereby being suitable for the neutral point unearth electric network and the neutral point arc suppressing coil earth electric network at the same time, and well adapts the condition of complex site, thereby ensuring fault diagnosis and correct line selection.

A DC matrix converter having six forward current conducting power switches and six reverse current conducting power switches has the on time duration of each power switch within each pulse width modulation period controlled by relationships between d, q components of a modulation index determined by the ratio of a voltage command to the instantaneous voltage of the AC mains expressed in stationary d, q coordinates, the selection of which is made based on inequalities between the AC mains voltage components expressed in dq coordinates, and relationships of the AC main voltage components expressed in d, q coordinates. Zero vectors are related to the one AC main having lower line-to-neutral voltage than the other AC mains, using relationships between the instantaneous AC mains voltage in d, q coordinates.

The invention discloses a distributing net single phase earth fault type and a distinguishing method of phase identification, relating to a distributing net single phase earth fault distinguishing method in the field of AC distributing net testing and relaying protection technology. According to the invention, through collecting three-phase voltage of the distributing net system and neutral point voltage of the distributing net system, phase angle of each eigenvector is computed through a special relation, the type of the fault and the phase identification can be fast distinguished through the phase angle distinguishing logic. The inventive working system is that a three-phase bus (000), a grounding transformer (100), a linear side of an arc suppression coil (200) are connected in turn with the earth; a controller (400), a thyristor (300) and a secondary side of an arc suppression coil (200) are connected in turn. The invention is simple in criterion, small in collection quantity, fast in distinguishing speed, high in accuracy, reliable in security, which is suitable for 3-66 KV distributing net based on an aerial line or a power cable.

A microcontroller determines the position of the rotor of a brushless, direct-current motor by determining the time of zero crossing of back electromotive force (EMF) emanating from the non-driven phase winding. The zero crossing point is determined by interpolating voltage differentials that are time stamped. Each voltage differential is the difference between the phase voltage of the phase winding and the motor neutral point voltage. The time of zero crossing is determined without using a comparator and without interrupting the processor at each zero crossing point. The processor interpolates the time of zero crossing independently of when the zero crossing point occurs. A hold signal conductor is connected both to a sample and hold circuit and to the load input lead of a time stamp register. The microcontroller simultaneously captures a phase voltage in the sample and hold circuit and a timer count in the time stamp register.

The invention discloses an intelligent dynamic power distribution network neutral-point grounding method and a complete device. The complete device comprises a grounding transformer (1), an arc suppression loop switch (2), a resistance loop switch (3), an adjustable reactor (4), a damping resistor (5), a damping resistor short-circuit switch (6), a resistor (7), a neutral-point voltage transformer (8) and a computer testing and control system (9). The intelligent dynamic power distribution network neutral-point grounding method and the complete device is technically characterized in that a power distribution network neutral-point grounding mode is dynamically converted from an arc suppression coil grounding mode into a small-resistance grounding mode. When the device is connected to a power grid or a power grid operation mode changes, the device firstly works in the arc suppression coil grounding mode. The device measures capacitive current, adjusts inductive current and enables IL-IC to be smaller than or equal to I delta, wherein the I delta is a preset residual current control value. When a single-phase grounding fault of the power grid occurs, the device outputs the inductive current to perform compensation and arc suppression to grounding fault current. If the fault is an instantaneous fault, the fault is eliminated through the compensation and the arc suppression. If the fault is a permanent fault and the grounding fault is still not eliminated after certain time T, the arc suppression coil grounding is converted into the resistance grounding mode, and a fault line is judged and disconnected by detecting zero-sequence current of feeder lines.

The invention discloses a tri-level four-leg T-shaped fault-tolerant converter and a control method thereof. The fault-tolerant converter comprises a DC input circuit, a tri-level T-shaped topology device, a failure isolation circuit, a redundant leg, a fault-tolerant bridge and an AC output circuit, wherein a power switch tube corresponding to the redundant bridge is controlled to be switched on in the normal operating state when the neutral-point voltage of a DC bus fluctuates sharply, the neutral-point voltage is quickly adjusted to be balanced by introducing inductive current, over-voltage breakdown of the power switch tube caused by sharp fluctuation of the neutral-point voltage is prevented, and a bidirectional controllable thyristor corresponding to the fault-tolerant bridge is controlled to be switched on to enable the redundant bridge to replace a broken bridge for fault-tolerant operation when a failure occurs. According to the fault-tolerant converter, fault tolerance of open circuit and short circuit failures of the switch tube and legs can be achieved, and output power and DC voltage utilization rate can not be reduced. The tri-level four-leg T-shaped fault-tolerant converter can be applied to an AC motor driving system or a grid-connected power generation system, so that the system has a better fault-tolerant operation function.

The invention discloses a method for detecting the position of a rotor of a brushless DC motor of a sensor without position by using the neutral point voltage. The structure of a rotor of the brushless DC motor takes the shape of a projecting pole, namely, the inductance Xd on a d axis of the rotor of the motor is not equal to the inductance Xq on a q axis of the motor. By detecting the neutral point voltage of a led-out winding of a stator of the brushless DC motor, the method of the invention can calculate the position of the rotor of the brushless DC motor with an energization mode each other, and the commutating time can be determined by lagging an electrical angle of 30 degrees. The method of the invention has the advantage of simple implementation of a back-electromotive force and is characterized in that the method takes no account of the motor revolution of an inductance method and can better determine the position of the rotor when the rotor revolution is close to from zero to the high speed as well as reliably and accurately commutate.

Power from a high voltage battery (10) (for example 36V) is supplied through an inverter (12) to a motor generator (14). A low voltage battery (20) (for example 12V) is connected through a reactor (18) to the neutral point of the motor generator (14). A voltage ratio of the low voltage battery (20) to the high voltage battery (10) is preferably from 1:2 to 1:4. In order to set the neutral point voltage to a desired charging voltage into the low voltage battery (20), the inverter (12) is controlled so as to follow a current distortion phenomenon. In this way, in a dual-power source system with a voltage ratio of a low voltage battery (20) to a high voltage battery (10) between 1:2 and 1:4, voltage switching means for use in charging a charge voltage of a high voltage side into a low voltage source can be implemented at low cost.

The invention provides a single phase grounding fault line selection method for medium voltage distribution networks based on fault process analysis, which comprises the steps of calculating neutral point voltage, determining whether the neutral point voltage exceeds a preset threshold value, diagnosing fault type, determining whether the fault is a single phase grounding fault, describing fault process, positioning line selection area, selecting line for the fault, outputting result and finishing. The method can reflect the process of fault development and evolution intuitively and constitutionally, effectively selects the line for stable grounding with single phase grounding fault time more than 500 milliseconds, and can totally capture and describe transient fault during the fault process.

Power from a high voltage battery (10) (for example 36V) is supplied through an inverter (12) to a motor generator (14). A low voltage battery (20) (for example 12V) is connected through a reactor (18) to the neutral point of the motor generator (14). A voltage ratio of the low voltage battery (20) to the high voltage battery (10) is preferably from 1:2 to 1:4. In order to set the neutral point voltage to a desired charging voltage into the low voltage battery (20), the inverter (12) is controlled so as to follow a current distortion phenomenon. In this way, in a dual-power source system with a voltage ratio of a low voltage battery (20) to a high voltage battery (10) between 1:2 and 1:4, voltage switching means for use in charging a charge voltage of a high voltage side into a low voltage source can be implemented at low cost.

The invention discloses a dual-closed-loop control-based active voltage arc extinction method and apparatus for a power distribution network in fault. The arc extinction method comprises the following steps of collecting a three-phase voltage and a neutral point voltage of the power distribution network, and judging whether the power distribution network suffers from a single phase grounding fault or not; if the power distribution network suffers from the single phase grounding fault, determining a fault phase according to the value of the three-phase voltage; injecting an initial current to the power distribution network to obtain a phase voltage and a neutral point voltage of the fault phase, and determining an optimal injection current through a dual-closed-loop control method; and injecting the optimal injection current to the power distribution network to realize arc extinction on an instantaneous single phase grounding fault. According to the method and the apparatus disclosed by the embodiments, based on the dual-closed-loop control method, a current is injected to the neutral point of the active arc extinction apparatus when the power distribution network suffers from the single phase grounding fault; and the fault phase voltage is controlled to be zero, and the reactive current component, the active current component and the harmonic component of the fault phase are compensated, so as to realize rapid and high-precision complete arc extinction on the instantaneous single phase grounding fault.

In related art technique, an average neutral point voltage is detected via a low-pass filter. Time constant of the low-pass filter must be set to cover the entire output frequency band of an inverter and voltage fluctuation due to modulated signal must be separated from that due to a short circuit to ground. According to the present invention, whether abnormality such as a short circuit to ground or to supply occurs in output lines can be determined based on an actual neutral point voltage of a motor, which changes in a stepwise fashion in conformity to a PWM pulse pattern output by an inverter device, and a normal neutral point voltage which depends on a PWM pattern output by the inverter device. Highly reliable abnormality detection in accordance with the waveform of the neutral point voltage and stable abnormality detection not depending on the inverter output frequency are feasible.

Problems with accuracy reading position detection signal peaks and minute phase differences in the detection current make motor drive control easily susceptible to differences in motor characteristics. The rotor position is determined based on whether or not a terminal difference voltage, which is the difference voltage between the motor terminal voltage and the pseudo-neutral-point voltage when the motor phases are selectively energized, exceeds a specific threshold value. The phase energized to start the motor is determined based on this determination and the motor is energized accordingly to start. Instead of switching directly from the search step at the initial rotor position to the back-EMF voltage mode, a search and start mode that creates initial rotor speed sufficient to start the motor is executed before entering the back-EMF voltage mode.

The invention discloses a brushless direct-current motor stator flux linkage identification method. The method comprises the following steps: the neutral point of a brushless direct-current motor is grounded to make the voltage of the neutral point clamped to zero; the brushless direct-current motor end voltage is determined through the on-off state of a power tube and a fly-wheel diode during the normal conduction process and the commutation process of a three-phase full-bridge inverter, wherein a three-phase phase voltage is obtained by performing subtraction between the three-phase end voltage and the neutral point voltage; detection is performed by adopting a current sensor to obtain a three-phase phase current, and calculation is performed according to the voltage model of the stator flux linkage to obtain a three-phase stator flux linkage; the three-phase stator flux linkage is filtered by a high-pass filter through CLARK transformation; and vector synthesis is performed on the three-phase stator flux linkage filtered by the high-pass filter to obtain a brushless direct-current motor stator flux linkage. According to the invention, advantages of less required motor parameters, simple structure, less calculation amount and low hardware cost can be realized.

The invention, which belongs to the power converter control field of the driving motor, relates to a method for controlling neutral point voltage balance of a three level converter, wherein the method is based on a voltage space vector pulse width modulation technology and is used for controlling a neutral point clamped three level inverter. The method comprises the following steps that: step one, an action time distribution factor of a redundant small vector is obtained; step two, an area where control on a neutral point potential balance can be realized by a nearest three vector (NTV) method is obtained; step three, an NTV action area in a mixed voltage space vector pulse width modulation method is obtained; step four, a switching condition of the mixed voltage space vector pulse width modulation method is designed; and step five, the mixed voltage space vector pulse width modulation method with a proportion of pm is realized. According to the invention, a redundant small vector distribution factor is employed to design a switching condition of a mixed voltage space vector pulse width modulation strategy; therefore, an essence of a space vector modulation method is embodied; themethod can be used flexibly and used variables are less, so that it is beneficial for analysis and development application.

To a neutral point of a motor is connected a positive electrode of an auxiliary battery and an auxiliary load. Voltage on a power supply line to the auxiliary load, a neutral point voltage, is detected, and disconnection of the auxiliary battery is determined when an increase of ripples in the neutral point voltage is detected. When a voltmeter cannot be used, control of the neutral point voltage is continued by measuring current of the auxiliary battery and performing control such that the current value becomes 0. A resolver is further provided on the motor for detecting the rotor angle with high accuracy. A control circuit generates, in accordance with an output of the resolver, a voltage control signal for each phase current having the same amplitude as the carrier amplitude during startup, and compares the voltage control signal to carrier to obtain a gate signal having the same frequency as the carrier frequency. In switching of the inverter, due to this gate signal, periods in which all phases are on or off are reduced, thereby preventing a large neutral point current.

The invention discloses a DC injection type route selection positioning system and a method thereof, which makes use of neutral-point voltage to ground to provide power supply for the generation of DC signal and inject DC to a fault system, and realizes faulty route selection and position by the detection of circulation of the DC signals. The structure of the invention comprises a grounding transformer, a DC generator, a control device and a fault indicator FD, wherein, the grounding transformer is connected with a system bus and injects the DC to the fault system by the primary coil of the grounding transformer; the DC generator is arranged between the primary-side neutral-point N of the grounding transformer and the ground; the control device is connected with the secondary side of bus-bar potential transformer to monitor whether a power distribution system has single-phase earth fault, control the switching of the DC, measure the injected DC at the same time and adjust the injected DC according to the measured injected DC; the fault indicator FD is positioned at the outlet of each feeder, and the fault indicator FD is also arranged at the feeder at intervals to detect the injected DC and select faulty line and locate the fault.

The invention discloses a system and a method for controlling neutral point voltage balance with a low frequency oscillation suppression function. The system comprises a multi-level inverter and a digital processing control module, wherein the digital processing control module comprises a sampling unit, a closed-loop control unit and a digital pulse width modulation (DPWM) unit; the output end of the DPWM unit is connected to each switching tube of the bridge arm of each phase of the multi-level inverter. The method comprises the following steps: in each switching period, the sampling unit acquires a direct-current bus voltage signal of the multi-level inverter, and a three-phase voltage signal and a three-phase current signal both output by the multi-level inverter, respectively; the acquired signals are processed by the closed-loop control unit to obtain three-phase modulating waves; the three-phase modulating waves are processed by the DPWM unit to obtain a pulse width modulation control signal which is used for controlling the working state of the switching tube of each phase of the multi-level inverter by virtue of a drive circuit. The system and the method are capable of suppressing the low frequency oscillation of the neutral point voltage of the direct-current bus of the multi-level inverter and realizing the neutral point voltage balance.

The invention discloses a three-level three-phase four-bridge arm converter which comprises a direct-current part, a converting part, a converting part controller, a fourth bridge arm and a fourth bridge arm controller, wherein the converting part is a diode clamp type three-level inverter, the fourth bridge arm is a T-type three-level structure, the exchange of energy at a direct-current side and an alternating-current side is realized by controlling the states of first three bridge arm power switching tubes of the converting part, and a neutral point voltage at the direct-current side is changed by controlling the state of a power switching tube of the fourth bridge arm to realize the balance of neutral point potential. The fourth bridge arm of the three-level three-phase four-bridge arm converter adopts a T-type three-level topology and omits 2 clamp diodes compared with the diode clamp-type three-level inverter, thus saving the cost, and being more balanced in power loss and higher in efficiency; the control of neutral point balance is not affected by a power factor, the modulation degree and a modulation strategy; and as the deviation permission range of the neutral point voltage at the direct-current side is controllable, the permission range can be adjusted according to actual working conditions to improve the efficiency of a system.

The invention discloses a real-time sensorless brushless motor phase change phase correction method based on the voltage of neutral points. By the adoption of the real-time sensorless brushless motor phase change phase correction method, the phase change position errors of a permanent-magnet brushless motor without a position sensor can be effectively reduced, and the optimum-position phase change is achieved. According to the real-time sensorless brushless motor phase change phase correction method, the voltage differences of neutral points within the 30-degree range on the front side and the 30-degree range on the rear side of a phase change point are collected and calculated so that the current phase error of the phase change can be determined, the voltage differences are used as phase change error feedback quantity, and real-time correction of the permanent-magnet brushless motor is achieved. Experiment results show that no matter whether the load is light or heavy, the phase change phase correction of the permanent-magnet brushless motor without the position sensor can be achieved.

The invention relates to a neutral-point voltage balance and common-mode voltage suppression method for a three-level inverter, and mainly provides a novel visual space vector modulation (VSVM) method. The method comprises the following steps: defining a new visual zero vector to just include zero vector 000; defining a novel visual small vector to be composed of an original negative small vector and two negative small vectors adjacent to the original negative small vector; and defining a new visual medium vector to be composed of an original medium vector and two medium vectors adjacent to the original medium vector. By using the space vector definition method, each composite vector cannot cause neutral-point voltage to be fluctuated, and basic vectors forming the novel visual space vector do not include positive small vectors and zero vector PPP and NNN, so that the output common-mode voltage is relatively small. When external nonlinear factors enable the neutral-point voltage to be fluctuated, on the basis of a new visual space vector modulation strategy, the action time distribution factors for each composite vector are appropriately adjusted by comparing the size of three-phase load current, so that neutral-point voltage balance is controlled.

The invention relates to a control method of a dual-active-bridge converter, and aims to provide a triple-phase-shift control method of the dual-active-bridge converter. According to the triple-phase-shift control method, an output voltage controller used for adjusting an output voltage is arranged in the dual-active-bridge DC converter of a bi-directional topological structure, an input signal ofthe output voltage controller is a difference value between a given value of a secondary side DC voltage and an actual measured value, and an output signal of the same is a control signal alpha whichis used for adjusting a duty ratio D1 of a primary side bridge arm neutral-point voltage, a duty ratio D2 of a secondary side bridge arm neutral-point voltage and a phase difference D3 of the voltages. The triple-phase-shift control method solves the problems of dual-active-bridge current stress optimal solution and control complexity, obtains the corresponding D1, D2 and D3 when the inductive current stress is minimum under each power point, solves relationships among the D1, D2, and D3, proposes the simple control method, and can realize the effect that the converter operates according to atrajectory with the minimum current stress by using just one PI controller.

The invention provides a method for controlling a brushless direct current motor. The method comprises the following steps that S1, the open loop of the brushless direct current motor is controlled to be started; S2, after the brushless direct current motor is started, the comparison signal of the three-phase end voltage and the neutral point voltage of the brushless direct current motor is detected; S3, the zero crossing point signal of the brushless direct current motor is judged according to the comparison signal of the three-phase end voltage and the neutral point voltage; S4, the position and the rotating speed of the rotor of the brushless direct current motor are obtained according to the zero crossing point signal of the brushless direct current motor; S5, the brushless direct current motor is controlled according to the position and the rotating speed of the rotor of the brushless direct current motor. According to the method for controlling the brushless direct current motor, position detection does not need to be carried out through a position sensor, the size and weight of the brushless direct current motor can be reduced, the development cost of the motor can be lowered, the motor can be controlled to be operated at high speed, and the reliability of motor operation can be improved.

Problems with accuracy reading position detection signal peaks and minute phase differences in the detection current make motor drive control easily susceptible to differences in motor characteristics. The rotor position is determined based on whether or not a neutral point difference voltage, which is the difference voltage between the neutral point voltage and the pseudo-neutral-point voltage when the motor phases are selectively energized, exceeds a specific threshold value. The phase energized to start the motor is determined based on this determination and the motor is energized accordingly to start. Instead of switching directly from the search step at the initial rotor position to the back-EMF voltage mode, a search and start mode that creates initial rotor speed sufficient to start the motor is executed before entering the back-EMF voltage mode.

To a neutral point of a motor is connected a positive electrode of an auxiliary battery and an auxiliary load. Voltage on a power supply line to the auxiliary load, a neutral point voltage, is detected, and disconnection of the auxiliary battery is determined when an increase of ripples in the neutral point voltage is detected. When a voltmeter cannot be used, control of the neutral point voltage is continued by measuring current of the auxiliary battery and performing control such that the current value becomes 0. A resolver is further provided on the motor for detecting the rotor angle with high accuracy. A control circuit generates, in accordance with an output of the resolver, a voltage control signal for each phase current having the same amplitude as the carrier amplitude during startup, and compares the voltage control signal to carrier to obtain a gate signal having the same frequency as the carrier frequency. In switching of the inverter, due to this gate signal, periods in which all phases are on or off are reduced, thereby preventing a large neutral point current.

The invention discloses a three-level VIENNA rectifier model prediction control system and method under a power grid unbalanced condition. The invention solves problems of the calculation of referencecurrent when the power network is unbalanced; the balance control of dc side voltage and DC side neutral point voltage; three-phase current zero-crossing distortion; control of unit power factor of grid current. The algorithm divides 25 voltage vectors into 6 sectors according to the current direction and 8 voltage vectors in each sector. Then five voltage vectors are selected according to the deviation of the neutral point voltage, and the optimal space voltage vector is obtained according to the value function, and the optimal space voltage vector controls the state of the switch transistor, so as to realize the control of the three-phase three-level VIENNA rectifier. The algorithm does not require the separation of positive and negative sequence of voltage and current, phase lock of voltage, current inner loop control module and modulation module when the power network is unbalanced.